Inductively coupled thermally responsive member



Feb. 15, 1966 c. E. GRYCTKO 3,235,690

INDUCTIVELY COUPLED THERMALLY RESPONSIVE MEMBER Filed July 6, 1964 2 Sheets-Sheet 1 m2- G; E55.

' [a IVVEVTOR 73 6/ 1 1 can E. yer/m Feb. 15, 1966 Filed July 6, 1964 C. E. GRYCTKO INDUCTIVELY COUPLED THERMALLY RESPONSIVE MEMBER 2 Sheets-Sheet 2 reazenmqflrang Q2723 219 United States Patent 3,235,690 INDUCTIVELY COUPLED THERMALLY RESPONSIVE MEMBER Carl E. Gryctko, Haddon Heights, N.J,, assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed July 6, 1964, Ser. No. 380,294 12 Claims. (Cl. 200-116) This invention relates to circuit breakers in general, and is a continuation-impart of my copending US. patent application Serial No. 133,879 filed August 25, 1961, entitled Inductive Birnetal Heater and assigned to the assignee of the instant invention. Specifically, the instant invention comprises a significant simplification over my aforementioned copending US. application in that the inductive heater for the thermal trip is singularly formed with the deflective bimetal thereof.

It is well known in automatic circuit breaker devices, and particularly in molded case circuit breakers, to form the automatic tripping device thereof of an instantaneous trip means in the form of a magnetic device and a time delay trip means in the form of a heated bimetal. For circuit breakers of relatively low current ratings, it had been the common practice to pass all circuit current directly through the bimetal for heating thereof. However, for circuit breakers of relatively high current ratings, this has proved impractical and various arrangements for indirectly heating the bimetal trip have been attempted.

One form which the indirect heater may take comprises a current carrying member of reduced cross-section in the vicinity of the bimetal. The reduced cross-sectional region, by offering increased resistance to the flow of electrical current therethrough, heats up. The heat generated Within this region is then transferred to the bimetal element to cause deflection thereof.

Other prior devices use various types of current transformer arrangements, with the circuit breaker current passing through the primary thereof. The transformer secondary may comprise a shorted turn around the transformer core with the bimetal element then connected to the secondary, and in this manner being heated as a function of the current in the secondary.

As current ratings increase, the above-noted prior art constructions have been found to be either impractical from the physical standpoint, or the costs have been excessive. These problems have been solved to a considerable extent by the arrangement shown in my aforementioned copending US. patent application Serial No. 133,- 879 which utilizes a direct inductive coupling between the deflectivebimetal and the current carrying strap of the breaker. This is achieved by surrounding the current carrying strap of the circuit breaker with a magnetic member inductively coupled thereto. The inductive effect due to the flux surrounding the current carrying strap .Will induce eddy current heating of the magnetic member. This heat is then thermally conducted to the bimetallic trip member, such that the thermally induced deflection thereof will operatively respond to the current flow within the circuit breaker unit.

In the constructions shown in my abovementioned copending US. patent application, a separate magnetic member was utilized as the inductively coupled heater member. An additional bimetal tripping member was then secured to the heater member, in thermal conductivity relationship therewith. In the instant application I advantageously combine these functions into a single member, thereby achieving increased simplicity, reliabil ity of operation, ease of fabrication and cost reduction.

In one form which my invention may take, the singular thermally responsive trip member may include an aperture for reception of the circuit breaker current carrying 3,235,690 Patented Feb. 15, 1966 strap. The thermally responsive member is formed of a plurality of layers that include a ferrous or magnetic material, in at least the region thereof surrounding the current carrying strap of the circuit breaker. Hence, the portion of the member surrounding the aperture forms the eddy-current loop, which is inductively coupled to the circuit breaker strap. The member also includes an elongated portion Which will be deflected upon heating, and is so positioned as to engage the circuit breaker trip mechanism corresponding to a predetermined extent of such deflection.

Other forms which my invention may take contemplate replacing the aperture with successive bends of the thermally responsive member wrapped about the current carrying strap. Similarly, the adjacent bends so provided will form an eddy-current heated loop of magnetic material about the circuit breaker current carrying strap.

The forms of the instant invention may be further modified to provide an air gap within the inductively coupled path surrounding the circuit breaker current carrying strap. This air gap will be of a predetermined configuration, so as to prevent premature magnetic saturation of the material within the heater portion of the thermally responsive member. That is, should saturation of the thermally responsive member otherwise tend to be reached under a continuous rated current condition, an increase to overload current would not increase the flux coupling and eddy current heating thereof. Hence, by so proportioning the air gap to avoid magnetic saturation under a continuous rated condition of the circuit breaker, this modification insures that should an overload condition occur, suflicient additional heating will be generated Within the heater portion to deflect the thermally responsive tripping portion of said singularly formed member.

As a further advantageous aspect of inductively heating the bimetal in accordance with the arrangements shown, the circuit breaker conducting strap may be of uniform cross-section throughout the length thereof. Be cause of this, heat transfer to the external conductors is not impeded.

It is therefore seen that the basic concept of the instant invention resides in combining the inductively related heater and the bimetallic deflective portion of the thermally responsive trip into a single unitary member which is formed of one piece. Such a singular member includes a first heater portion which surrounds the current carrying conductor of the circuit breaker, and is inductively coupled thereto; and a second elongated bimetal portion to effect desired tripping action of the circuit breaker device.

Accordingly, a primary object of this invention is to provide a circuit breaker device, wherein the time delay trip element thereof is of a simplified construction.

Another object of this invention is to provide an inductive coupling relationship between a thermally responsive deflective member and a current carrying strap, wherein an inductively coupled portion of said member is singularly formed with the heat responsivedeflective portion thereof.

' A further object of this invention is to provide a singularly formed thermally responsive trip member having a first portion for inductive coupling to a current carrying conductor, and a second portion to be deflected, corresponding to eddy current inductive heating of the first portion thereof.

Another object of this invention is to provide such a thermally responsive trip member wherein an air gap of predetermined configuration is provided within the eddy current path of the first portion thereof, so as to prevent magnetic saturation under normal current flow within the current carrying conductor.

Still another object of this invention is to provide within a circuit breaker a singularly formed thermally responsive trip member having a first portion for surroundingly receiving the current carrying strap of the circuit breaker in inductive coupling relationship therewith, and a second elongated portion to be deflected corresponding to inductive heating of the first portion thereof.

These as well as other objects of this invention "will readily become apparent upon a consideration of the following description of the accompanying drawings, in which:

FIGURE 1 is a simplified'perspective view illustrating a first form of the instant invention, wherein the current carrying strap "passes through an aperture of the thermally responsive member.

FIGURE 2 is a similar perspective view of a modified form which my invention may take, wherein an air gap of predetermined configuration is provided.

FIGURE 3 shows still another form of my invention, wherein the aperture is replaced by a successive series of surfaceswrajpped about the current carrying strap to define the inductively coupled magnetic loop.

FIGURE 4 is a modification f the form of the instant invention shown in FIG. 3, but wherein an air gap 'is provided within the inductively coupled magnetic 'path about the current carrying strap.

FIGURE 5 is a longitudinal cross-sectional view of a molded case circuit breaker illustrating the current carrying path through the centerphase of a typicalthree-lphas'e molded case circuit breaker with the time delay trip element thereof being heated by the arrangement of the type shown in FIG. 1.

FIGURE 6 is a plan view of the automatic trip element of 'FIG. 5. p v j V I Referring to the figures and more particularly FIGURE 1, there is shown a current carrying bar or strap 100, which may correspond to a current carrying member within a molded case circuit breaker device. Conductor :strap 1'00 passes through a'pertured opening 115 of singularly formed thermally responsive member 110. Thermally responsive member 110 is fixedly secured to conductor 100, by forming a foot 122 from the material lanced out "of opening 115 and securing it to conductor 110 at 121 as by a weld or rivet. Alternatively, the thermal element 110 may be sealed in suitable formations of the circuit breaker housing (not shown), withit merely being necessary that "conductor 100 pass throughopening 115. Thermally responsive member 110 is formed of a plurality of individual metallic layers (bimetal or trimetal) that include a ferrous or magnetic material in one or all of the layers in at least the region about current carrying conductor 100. Hence, a magnetic region is formed about'current'carrying conductor 100 having circulating eddy currents generated about the flux path shown by thedotted line 117.

An elongated portion of the thermally responsive bimetallic member 110 extends from the region containing aperture 115, and contains an adjustable screw 120 at its terminus. This elongated region'corresponds to the conventional type of bimetallic member withinthe time delay trip unit'of a circuit breakerdevice. Its deflection will bring about engagement with extension 125 in accordance with the desired tripping characteristics, with such en'- gagement serving to release the tripping cradle and-bring about automatic tripping of the circuit breaker 'unit.

In operation such'de'flectionis caused by circuit breaker alternating current flowing through bar 100 along the path indicated by line A. This in turn generates or produces eddy currents on planes at right angles to the flux path shown by arrow 117, so as to inductively heat member 110. The heat generated at this portion of member 110 'is thermally conducted to the elongated upstanding portion thereof, so as to effect bimetallic deflective action thereof in the conventional manner. Member 110 will be calibrated in accordance with stanadard techniques,

4- such that current in excess of a predetermined magnitude flowing through bar for a predetermined length of time will cause sufficient deflective movement of the thermally responsive member 1113 so as to bring it into engagement with tripper extension 125 to initiate automatic tripping of the circuit breaker *unit.

FIGURE 2 illustrates a somewhat modified arrangement wherein portions of the thermal trip corresponding to that previously described in conjunction with FIG. 1 are indicated by a 1 suffix. Thermally responsive member -1 is similarly inductively coupled to current carrying bar 101) via aperture -1, with an air gap 119 now provided within the magnetic path 1 17-1. The air gap 119 is preferably provided to prevent magnetic saturation of the path 117-1 corresponding to a continuous rated value of high current flowing within current carrying circuit breaker strap 100. Should saturation have been reached at 'such a normal value of current flow, a further increase in current corresponding to a moderate overload condition would not result in an increase in magnetic flux within the magnetic path 117-1, such that additional deflective movement of screw -1 would not take place corresponding to such an overload condition. Hence, air gap 119 is of a predetermined configuration and extent, so as to prevent premature saturation of the magnetic path 117-1.

FIGURES 3 and 4 show a 'somewhat'modified arrangement of the instant invention, wherein instead of provid ing an aperture within the thermally responsive member, a series of successive portions thereof are wrapped about the current carrying strap 101). Those portions corresponding to that previously described in conjunction with FIGURES -l and 2 are indicated in FIGS. 3 and 4 by -2 and -3 suffixes respectively. Thermally responsive menrbe-rs 110-2 or 110-3 thereof .may be secured to current carrying strap 10% as by spot welding or a rivet -'at point X. The wrapping about of the thermally responsive mem bers 110-2 and 110-3 are provided by the "similar successive portions 111, 112, 113, 114 and 11 6. A right angle bend 118 defines the upstanding elongated portion which will be deflected into engagement with tripper upon inductive heating thereof. 1

As shown in FIG. 3, member 110-2 is wrapped'about current carrying strap 100, with its higher expansion side being on the outside. In this manner, the deflective movement of the end thereof will be to the right, and eifec'tive through the entire elongated length thereof. Al-terna tively, member 110-2 maybe wrapped about current car- -rying conductor 1110, with its higher expansion side being adjacent said conductor. 'If so the deflection will alternatively be to the left, and the effective length thereof will be increased to include the entire length of member 110-2 to its point X, whereat it is physically fastened 'to current carrying conductor 1%. If desired, an air gap 119-1 may be provided.

FIG. 4 shows a modified version of the arrangement shown in FIG. 3, wherein an air gap 119-2 is now pro vided within the magnetic path 117-3, and acting in a similar fashion as gap 1190f FIG. 2 and 119-1ofFIG. 3, to prevent magnetic saturation under normal current conditions. To provide this air gap 119-2, wrap around portion "lld'extends above the uppersurface'of conductor strap 100, such that adjacent portion 116 'will be similarly located above the conductor. Sides '112 and 113 are also shown space-separated from the conductor so that the wrapping of thermally responsive member 110-3 about the current carrying conductor 100 is loose. As shown in this figure, the high expansion side of the element is about the outer periphery, with deflection of the 'elongated end thereof being to the right. Also, by virtue of the loose Wrapping about the inductivelycoupled portion of the member, the effective deflective length will include sides 116, 1 14, 113, 112, and 111 to point X.

Reference is now made to FIGS. 5 and 6, which show the time delay tripping element in accordance with the embodiment of FIG. 1, incorporated within a conventional type of molded case circuit breaker unit.

Circuit breaker 1 is typically a three phase unit including a molded housing comprising base 11 and removabl cover 12 partitioned into three parallel elongated chambers with' only the center chamber being illustrated. Each chamber houses identical current carrying elements, one for each phase of the circuit breaker, and in addition the center chamber houses a single contact operating mechanism 30 for all three phases.

Each of the current paths comprises load terminal connector 16, load terminal strap 17 having loop forming portions 18 and 100, lug 22, flexible member 23, movable contact arm 24, movable contact 25, stationary contact 26, line terminal strap 27 and finally tulip-type terminal connector 28 secured by screw 29 to line terminal strap 27. Are chute 40 is positioned to receive electric current arcs drawn between cooperating contacts 25, 26 upon parting thereof.

Mechanism 30 for contact operation is of type well known to the art and is completely described in the copending application of E. Wortmann, Serial No. 108,812, filed May 9, 1961, entitled U-Shaped Cradle for Circuit Breaker." Briefly, operating mechanism 30 includes handle 98 which projects through cover opening 90 for manually operating cooperating contacts 25, 26 into and out of engagement. Handle 98 is mounted to the web of inverted U-shaped member 33 which is pivotally mounted at 32 to U-shaped frame 31. A pair of main springs 34 extend from the web of U-shaped member 33 to triangular member 35 which is pivotally mounted to the knee 37 of the toggle linkage comprising links 38, 39.

The lower end of the link 39 is pivotally connected at 42 to bracket 43 which carries contact arm 24. The up per end of link 38 is pivoted at 41 to latchable cradle 50. Transverse tie bar 99 extends through all three of the housing compartments and carries the brackets 43 of all three phases so that the movable contacts 25 of all three phases are simultaneously operated into and out of engagement with their cooperating contacts 26.

I Cradle 50 carries latch member 51 engageable with portion 52 of auxiliary latch member 53 which is pivoted to frame 31 at 54. Latch 55' of auxiliary latch member 53 is engageable with main latch member 55 carried by transversely extending common tripper bar 56. When tripper bar 56 is pivoted clockwise latch tip 55' is released, in turn releasing latch member 51, thereby permitting cradle 50 to pivot counterclockwise about its pivot 51a to collapse toggle 38, 39 so that springs 34 separate contacts 25, 26.

Portion 18 of the terminal strap extends through U- shaped instantaneous trip magnet 61 which is secured to base 11 by screw 62. Instantaneous trip armature 63 is pivoted at its lower end against magnet 61 and is biased in a clockwise direction by tension springs 64, one end of which is connected to bracket lug 65 and the other end of which is connected to lug 66 of armature 63. When armture 63 is attracted by magnet 61 adjusting screw 67 carried at the upper end of armature 63 engages the downward extension 68 of tripper bar 56 to cause a clockwise rotation thereof for releasing of the circuit breaker latches.

Portion 100 of the terminal strap extends through apertured opening 115 of the thermally responsive member 110, in the manner shown in FIG. 1. The upper end of member 110 carries adjustable screw 120, which is engageable with the upward extension 125 of tripper bar 56.

In a manner previously explained in conjunction with FIG. 1, circuit breaker current carried by portion 100 of load terminal strap 17 induces eddy currents to flow in singularly formed thermally responsive member 110, which is constructed of a ferrous or magnetic material, in at least the region surrounding current carrying strap 100. These eddy currents produce heating of the lower 6 region of member with the heat being conducted along the entire elongated length thereof so as to cause a deflection of adjustable screw to the right as shown inFIG.2.

When the current through conductor 17 and hence portion 100 thereof exceeds a predetermined value on a time-current basis, adjusting screw 120 will move sufficiently to the right to engage tripper bar upper extension causing tripper bar 56 to rotate clockwise thereby releasing the latches as previously explained.

At this time it is noted that terminal strap 17 is of uniform cross-section throughout the entire length thereof. There is no need to reduce the cross-section terminal strap in the region thereof adjacent to thermally responsive member 110. Thus, conduction of heat, produced in housing 11, 12, to terminal connectors 16 and 28 and to the external conductors (not shown) will not be impeded.

Thus, my invention provides a thermally responsive trip elements for a circuit breaker of an extremely simplified construction, wherein the inductively coupled heater and bimetallic deflective portions thereof are combined into a single member.

In the fore-going specification, the instant invention has been described in conjunction with preferred embodiments thereof. Many variations and modifications will now become apparent to those skilled in the art, and it is preferred therefore that the instant invent-ion be limited not by the specific disclosure herein contained but only by the appended claims.

I claim:

1. A circuit breaker including a first and a second terminal, means for connecting said terminals including cooperating contacts and a conducting strap serially connected to each other, a mechanism for operating said contacts into and out of engagement, and trip means connected to said mechanism for automatic tripping thereof upon the occurrence of predetermined abnormal circuit conditions, said trip means including a thermally responsive means, formed from one piece as a single unitary member; said member including a loop portion inductively coupled directly to said strap and heated through the action of current flowing in said strap, and a portion extending therefrom and positioned for deflection responsive to said heating.

2. A circuit breaker including a first and a second terminal, means for connecting said terminals including cooperating contacts and a conducting strap serially connected to each other, a mechanism for operating said contacts into and out of engagement, and trip means connectedto said mechanism for automatic tripping thereof upon the occurrence of predetermined abnormal circuit conditions, said trip means including a thermally responsive means, formed from one piece as a single unitary member, said member having at least first and second layers formed of metals having differing temperature characteristics to define a bimetallic element portion; said member also having a heater portion, including an aperture; said strap passing through said aperture whereby said member is inductively coupled to said strap and heated through the action of current flowing in said strap.

3. A circuit breaker including a first and a second terminal, means for connecting said terminals including cooperating contacts and a conducting strap serially connected to each other, a mechanism for operating said contacts into and out of engagement, and trip means connected to said mechanism for automatic tripping thereof upon the occurrence of predetermined abnormal circuit conditions, said trip means including a thermally responsive means, formed from one piece as a single unitary member; said member including a loop portion inductively coupled directly to said strap and heated through the action of current flowing in said strap, and a portion extending therefrom and positioned for deflection responsive to said heating; said member having a substantially uniform cross-sectional area throughout the length thereof.

4. A circuit breaker including a first and a second terminal, means for connecting said. terminals including cooperating contacts, and a conducting strap serially connected tov each other, a mechanism for operating said contacts into and. out of engagement, and trip means. connected to said mechanism for automatic tripping thereof upon the occurrence of predetermined abnormal circuit conditions, said trip means including a thermally responsive means, formed from one piece as a single unitary member; said member including a loop portion inductively coupled directly to said strap and heated through the action of current flowing in said strap, and a portion extending therefrom and positioned for deflection respons-ive. to said heating; said loop portion comprising a loop of magnetic material with said strap passing therethrough; said loop including a gap of predetermined configuration to prevent m'agnetic saturation of said member under normal load conditions.

5. In a circuit breaker the combination comprising an element through which circuit breaker current passes, a fault responsive trip means, fromed from one piece as a single unitary member, said single member including a loop portion inductively coupled to said element and having eddy currents induced therein by current flow in said element, said eddy currents causing heating of said member, said member including a trip element portion in heat conducting relationship with respect to said loop portion whe eby the eddy current heating thereof is effective to cause heating of said trip element portion and operation thereof to automatically trip the circuit breaker when current in saidelement exceeds a predetermined value; said single member comprised of a plurality of layers, including magnetizeable material at said loop portion, and a bim-etal portion forming said trip element portion.

6. In a circuit breaker the combination comprising an element through which circuit breaker current passes, a

fault responsive trip means, formed from one piece as a 7 single unitary member, said single member including a loop portion inductively coupled to said element and having eddy currents induced'therein by current flow in said element, said eddy currents causing heating of said member, said member including a trip element portion in heat conducting relationship with respect to said loop portion whereby the eddy current heating thereof is effective to cause heating of said trip element portion and operation thereof to automatically trip the circuit breaker when current in said element exceeds a predetermined value; said single member comprised of a plurality of layers, including magnetizable material at said loop portion, and a bimetal portion forming said trip element portion; said loop portion positioned about said element, with said element passing therethrough; said loop including a gap of predetermined configuration to prevent magnetic saturation of said-member under normal load conditions.

7. The combination comprising a current carrying bus,

a single unitary member formed from one piece, including a magnetic loop portion and a thermally responsive portion, said a magnetic loop portion inductively coupled to said bus whereby current in said bus induces eddy currents in said member to cause heating thereof, said thermally responsive portion heated by heat produced by eddy currents at the loop portion of said member, heating of said thermally responsive portion in excess of a predetermined level being effective to move a selected portion of said thermally responsive portion to a required position for performing of a desired function.

8. The combination comprising a current carrying bus, a single unitary member formed from one piece, including a magnetic loop portion and a thermally responsive portion, said a magnetic loop portion inductively coupled to said bus whereby current in said businduces eddy currents in said member to cause heating thereof, said thermally responsive portion heated by heat produced by eddy currents at the loop portion of said member, heating of said thermally responsive portion in excess of a predetermined level being effective tomove a selected portion of said thermally responsive portion to a required position for performing of a desired function; said thermally responsive portion comprising an elongated multilayered region of said member, a first end of which is singularly formed with said magnetic loop portion, and a secondend of which is located to deflect upon eddy current heatingof said member.

9. A circuit breaker as set forth in claim 1, wherein.

said member having .a substantially uniform cross-sectional area throughout the width thereof.

10. A circuit breaker as set forth in claim 1, wherein 12. A circuit breaker as set forth in claim 2, said member having a substantially planar configuration, and said aperture is an opening within said plane adapted to receive said conducting strap.

References Cited by the Examiner UNITED STATES PATENTS 1,110,152 9/1914 Steen 200-122 X 2,340,957- 2/ 1944 Grissinger 200-88 2,939,929 6/1960 Hobson 200-88 FOREIGN PATENTS 151,064 2/ 1932 Switzerland.

BERNARD A. GILHEAN-Y, Primary Examiner. 

1. A CIRCUIT BREAKER INCLUDING A FIRST AND A SECOND TERMINAL, MEANS FOR CONNECTING SAID TERMINALS INCLUDING COOPERATING CONTACTS AND A CONDUCTING STRAP SERIALLY CONNECTED TO EACH OTHER, A MECHANISM FOR OPERATING SAID CONTACTS INTO AND OUT OF ENGAGEMENT, AND TRIP MEANS CONNECTED TO SAID MECHANISM FOR AUTOMATIC TRIPPING THEREOF UPON THE OCCURRENCE OF PREDETERMINED ABNORMAL CIRCUIT CONDITIONS, SAID TRIP MEANS INCLUDING A THERMALLY RESPONSIVE MEANS, FORMED FROM ONE PIECE AS A SINGLE UNITARY MEMBER; SAID MEMBER INCLUDING A LOOP PORTION INDUCTIVELY COUPLED DIRECTLY TO SAID STRAP AND HEATED THROUGH THE ACTION OF CURRENT FLOWING IN SAID STRAP, AND A PORTION EXTENDING THEREFROM AND POSITIONED FOR DEFLECTION RESPONSIVE TO SAID HEATING. 